1. Field of the Invention
The present invention relates to a semiconductor device and particularly to a semiconductor device on which a drive circuit that drives an external device is formed.
2. Related Art
Generally, semiconductor devices on which a drive circuit that drives an external device is formed (mounted) are known. For example, there are microcomputers on which an LCD panel driver that is a drive circuit for driving a liquid crystal display (LCD) is formed. FIG. 6 shows the general configuration of one example of a conventional microcomputer on which an LCD driver panel is formed.
The semiconductor device 100 shown in FIG. 6 is equipped with an LCD panel driver 112, a VPP generating circuit 121, a flash memory 122, a reference voltage circuit 124, a VLCD step-up circuit 128, and a logic circuit 130.
The reference voltage circuit 124 generates a reference voltage VREF by an inputted power supply voltage VDD. The VLCD step-up circuit 128 boosts the inputted reference voltage VREF to a drive voltage VLCD and outputs the drive voltage VLCD to the LCD panel driver 112. The flash memory 122 stores various programs and so forth.
The flash memory 122 executes three types of operations—an erase operation, a program operation, and a read operation—as operation modes controlled by an operation instruction from the logic circuit 130. In contrast to when the flash memory 22 performs the read operation, the flash memory 22 cannot perform the erase operation and the program operation unless a high voltage is supplied thereto. For that reason, the step-up circuit generates a voltage according to the operation of the memory and supplies the voltage to the memory in accordance with the operation. For example, Japanese Patent Application Laid-Open (JP-A) No. 2000-67591 describes a voltage generating circuit that is a step-up circuit for a memory that generates a voltage according to each operation of the memory.
In the case of the conventional semiconductor device 100 shown in FIG. 6, when the flash memory 122 performs the read operation, it can execute that operation by only the supply of the power supply voltage VDD, but when the flash memory 122 performs the erase operation or the program operation, it cannot execute those operations unless a voltage VPP that is a high voltage is supplied apart from the supply of the power supply voltage VDD. For that reason, when the flash memory 122 performs the erase operation or the program operation, the VPP generating circuit 121 boosts the power supply voltage VDD to the voltage VPP and supplies the voltage VPP to the flash memory 122.
In this way, because the VPP generating circuit 121 is needed as a step-up circuit for supplying a voltage according to the operation of the flash memory 122, an increase in the chip size resulting from the circuit scale occurs. Because of this, there have been cases where problems such as a cost increase, for example, arise.